The invention relates to a cylinder head gasket used in an engine, and more particularly, to an improvement in a cylinder head gasket having a shim which surrounds a combustion chamber opening.
A cylinder head gasket is generally known in the art which is of the type having an annular metallic shim welded to a flat portion around a combustion chamber opening formed in a metal plate. A cylinder head gasket is also known in the art (see Japanese Laid-Open Patent Application No. 317,890/1997) which comprises an annular groove which surrounds a combustion chamber opening formed in a metal plate, an annular shim fitted into the annular groove, and an annular bead located outwardly of the shim and projecting in the same direction as the shim.
Recently, as a higher efficiency is required of an engine, the engine combustion temperature has risen. With an increase in the combustion temperature, there is an increased temperature differential between cold and hot states of the engine, thus increasing the differential thermal expansion between a cylinder block and a cylinder head. With a former type mentioned above in which a metallic shim is welded to the flat portion, a continuous welding or a multi-layer welding must be applied in order to secure adequate mounting strength. However, such a welding results in an increase in the manufacturing cost obviously, and in addition, the heat applied during the welding operation causes an increased distortion of the shim and the plate itself, thus degrading the sealing capability and presenting a difficulty when assembling it into an engine.
With the latter type disclosed in the cited Application, the use of a resin material for the shim may give rise to a problem in respect of the heat resistance when the combustion temperature is high.
In view of the forgoing, the present invention provides a cylinder head gasket which is preferred for use in an engine of a higher combustion temperature than in the prior art.
Specifically, in a cylinder head gasket which is constructed in the similar manner as a conventional cylinder head gasket, in accordance with the present invention, an annular projecting step is formed from the metal plate so as to surround the combustion chamber opening to thereby define the annular groove inside the projecting step, and the shim which is fitted into the annular groove is formed of a metal material and is welded to the plate in an interrupted manner circumferentially.
With the arrangement of the invention, while the shim is welded to the metal plate in an interrupted manner, the differential thermal expansion which acts on the shim is resisted to a degree by the side wall of the annular groove, and hence the intermittent welding, which provides an inferior mounting strength as compared with the continuous welding or the multi-layer welding, can be employed.
As a consequence, the required cost can be reduced as compared with the use of the continuous welding or the multi-layer welding. In addition, the thermal deformation which occurs in the shim and the plate itself can be reduced as compared with the use of the continuous welding or the multi-layered welding, enabling the sealing capability to be improved.
A shim formed of a metal material exhibits a higher heat resistance than a shim which is formed of a resinous material, and is preferred for use with an engine of a higher combustion temperature than in a conventional cylinder head gasket which uses a shim formed of a resinous material.
Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the attached drawings.